The purpose of this study is to determine the phenotype of multiple extracellular matrix molecules in adult mouse glomeruli from different strains of mice. We used the increased sensitivity afforded by the polymerase-chain reaction to assess `1 type I and several ` chains of type IV collagen mRNA as well as laminin subchains in freshly microdissected normal adult mouse glomeruli. RT-PCR reactions for mRNA encoding these components were also performed using mesangial cell lines previously isolated from the same strain of mice. Type IV collagen mRNA was easily detectable in normal adult mouse glomeruli as well as in the cell lines. Assays using competitive PCR were developed. The current study provides evidence that the expression of types I and IV collagen in normal glomeruli is regulated at the pretranslational level in vivo. We have applied this method to a mouse strain which develops spontaneous glomerulosclerosis, the ROP-OS mouse. This mouse is originally derived from a radiation-induced mutation. Our preliminary data indicate that the mutation induces a rapid glomerulosclerosis on a ROP background but has little effect on a C57Bl background. The ROP-OS mouse has a 3 fold increase in mRNAs coding for type IV collagens and laminin early in life at a time when morphologic evidence of glomerulosclerosis is quite discrete. This model allows the study of ureteric bud branching in renal development, and the relationships between glomerular number, size and sclerosis.